The present invention is directed to a position detection system integrated with a mobile terminal and a method to shorten time required to secure an accurate estimation of position.
Mobile terminals such as cellular phones, personal digital assistants, automobiles with GPS equipment, laptops equipped with wireless modems, and the like have exploded into the public consciousness. These devices enable individuals to remain connected to other people without being tied to a land-based phone.
Because mobile terminals are in fact, by definition, mobile, many recent patents have discussed incorporating position detection capabilities into the mobile terminals so that the user of the mobile terminal may know where they are. Alternatively, such technology may be used so that a third party knows where the mobile terminal is located. One such proposed use of a position detection system is to deter theft; items being protected may periodically report their present whereabouts through a wireless modem as determined by the position detection system.
One popular position detection system targeted for such incorporation into a mobile terminal is the Global Position System (GPS), which relies on a constellation of satellites to assist a GPS receiver in determining its location. Other satellite-based systems do exist, such as GLONASS, the Russian equivalent of GPS.
Unfortunately, while integration of position detection systems and mobile terminals seems like a laudable goal and is technically feasible, such integration may tend to ignore the realities behind such position detection systems and mobile networks. For example, GPS has an extremely slow data transfer rate. It takes on the order of ten to twenty minutes to secure all known data from the satellites. While GPS may be an extreme example, other positioning systems may experience similar delays. Inability to secure quick position information may lead to consumer frustration. In a theft deterrent usage, the long lag in determining a position of a stolen item may hinder recovery efforts. Furthermore, such a slow transfer rate means that the mobile terminal must be active for that entire time, creating a drain on its battery.
Several solutions to this problem have been proposed, although presently without any significant commercial exploitation. In one solution, the mobile terminal gets some or all information from the mobile network. One aspect of this solution requires that the mobile terminal inquire over the mobile network to a server about the precise present location (xe2x80x9cephemerisxe2x80x9d) of the satellites. A problem arises for this solution when the mobile network may be unable to supply this information. This may occur, for instance, when users roam into new areas and the local service provider is not capable of providing the required assistance. In a second aspect of this solution, the mobile network continuously provides almanac information over a control channel. This creates a bandwidth drain for sporadically used information and is inefficient.
As a fallback position, the mobile terminal may still receive the information from the satellites themselves, but this, as previously noted is an extremely slow and battery intensive process. Additionally, the mobile terminal may never have been in an active state long enough to download the almanac information from the satellites. This may be because the user is selective about powering on the mobile terminal or because the mobile terminal has previously been able to acquire the almanac information from the service provider and has never had to access the satellites for almanac information.
Still another solution is to hardcode the almanac information into the mobile terminal. However, this information may become dated after a few months and no longer serve its intended purpose as satellite orbits may vary with time. Since the information is hardcoded, the mobile terminal would require a new circuit board or software update to access new information.
Thus, there remains a need for a mobile terminal that can selectively store almanac information for later use without requiring the power drain associated with downloading the information from the satellites and without wasting bandwidth on the control channels of the service providers.
The present invention uses ephemeris information to compute satellite positions for faster acquisition at a later time. In one embodiment, the present invention creates an almanac in the memory of the mobile terminal by converting ephemeris information into almanac information. The conversion may comprise merely scaling the ephemeris information and perhaps losing a few bits of information. The ephemeris information may be received from either the satellites or the mobile network. The ephemeris information may be received from the mobile network by the mobile terminal by one of a number of different techniques. The mobile terminal may periodically request the ephemeris information. The mobile network may continuously or periodically broadcast the ephemeris information at a low rate, thereby conserving bandwidth. Other techniques are also contemplated.